Lake Name:

a lake.

Blue-green algae blooms appeared earlier and on more lakes this summer than usual. Learn more about these blooms and the health risks they can pose.

Contact information
For information on Lakes in Wisconsin, contact:
Wisconsin DNR Lakes
Division of Water
Bureau of Water Quality
Blue-Green Algae Contacts

Blue-Green Algae

Recreational Water Concerns

Can water containing blue-green algae blooms be used for recreational activities?

Because local health officials cannot easily determine when blue-green algal toxins are being produced, anyone considering recreation on or in the water should use common sense. Simply put, if a scum-layer or floating mat is present, do not recreate in or on that water. The chance for health effects is greater if you or your children participate in water-related activities such as swimming, wading, water or jet-skiing, or wind surfing. Try to find areas where a blue-green algae bloom is not present.

Is it safe to let your children or pets swim in ponds (e.g., farm ponds, stormwater detention ponds, golf course ponds)?

By design, many farm ponds, golf course ponds, and stormwater detention ponds are constructed to trap nutrients, eroded soil, and other debris. By doing so, they prevent such materials from reaching nearby lakes, ponds, and streams. But because more nutrients may be available and because these types of ponds are generally more shallow and warm, it is possible for them to experience more frequent blue-green algae blooms (which may produce toxins). Again, a common sense approach is recommended for such ponds: if a scum layer or floating mat is present, do not let your children or pets swim.

Is there a risk to SCUBA divers who swim in blue-green algae blooms?

It may not always be possible to avoid swimming in blue-green algae blooms. Rescue SCUBA divers may be required to swim in areas where a bloom is present. In those cases, divers should try to minimize the ingestion of water during the course of the dive. Divers should also shower or rinse off thoroughly after exiting the water, and clean all gear after use. Divers who show any signs of illness after exposure should seek medical attention.

Do blue-green algae pose a risk to competitive swimmers such as triathletes?

When organizers establish the schedule and pick a course for a triathlon, they have no way of knowing whether or not a blue-green algae bloom will be present in the swim area. To the degree possible, race organizers are encouraged to establish a course that minimizes the exposure of participants to blue-green algae blooms. Race organizers may also want to consider having a rinse station established near the swimming finish area. All participants are encouraged to minimize the ingestion of water during the course of the event. As is the case in any organized race, participants should seek medical attention if they show any signs of illness during or after the event.

Fish Consumption Concerns

Can I eat fish from water containing blue-green algae?

Some blue-green algal toxins have been shown to accumulate in the tissues of fish and shellfish, particularly in the viscera (liver, kidney, etc.). Whether or not the accumulation levels are sufficient to pose a risk to humans is uncertain, although it would depend in part on the levels of consumption and on the severity of the blue-green algae blooms where the fish or shellfish were caught or collected.

The World Health Organization advises that people who choose to eat fish taken from water where a blue-green algae bloom is present eat such fish in moderation and avoid eating the guts of the fish, where accumulation of toxins may be greatest. Also, take care to not cut into organs when filleting the fish and rinse the fillets with clean water to remove any liquids from the guts or organs before freezing or cooking.

Important Note About Hygiene

All natural surface waters contain bacteria, algae, viruses, and other pathogens that if consumed may pose health risks to humans, pets, and other domestic animals (e.g., cattle, swine). No one should ever ingest raw water.